I have been using a di-GPS Eco Prosumer m, mounted on my camera. No cables, just a connector on the side of the camera. It works fine, however it's not always that exact in urban areas between buildings, it can differ up to 100 m. Before it finds the position, it can report the North Pole.
It can take some time to find a new location or if it not been used for a time, it has to get some satellite data to figure it out. There's a little green LED on it that flashes when searching that becomes solid green when the position is established.
It uses the camera's battery, no battery inside the di-GPS. Be careful not to put the camera down, leaning on the di-GPS on the left side, or you can break the circuit board inside the camera.
But once you comes with terms with the small glitches it works fine, I have used mine for over 10 years, on my D7000/7200/Z6/Z6iii, latest on my trip to south-east Asia. The position can be seen on Google Earth, via Lightroom.
GPS for Nikon
www.dawntech.co.uk